Exercise devices which attach to the shoes of a user are known in the art. These devices can be utilized to strengthen the muscles of the foot and lower leg, to shape and tone the calves and thighs, and to improve balance. Some of these devices employ the principal of plyometrics with a view toward improving sports performance. In pylometrics muscles are loaded and then contracted in rapid sequence. A rapid muscle lengthening movement (eccentric phase) is followed by an explosive muscle shortening movement (concentric phase). Some of these devices also improve proprioception, which is one's sense of the relative position of neighboring parts of the body.
Randomization plays an important role in training. The human body has evolved to adapt to different stresses so that it can quickly recover and survive. During a workout muscles are torn down with the purpose of building them back up. However, the body will adapt to an exercise routine and it becomes very difficult to achieve gain by tearing the same muscles down with the same exercises. As such, a training plateau is reached. However, by using a randomized training process, the muscles continually undergo different and random stresses and the training plateau is raised. To this end, balance balls were introduced with great acceptance for applying randomization to core & upper body exercises. There are different balance boards and wobble boards that do a similar, but less effective job than the balance ball. The problem is that most people can't stand on a balance ball while doing their exercise.